The invention relates to a printing device, in particular to a franking and/or addressing machine, with a print head which is held displaceably on a print-head holder. In order to achieve the relative movement between a print head and a medium to be printed, the print-head holder is configured such that, during printing, it can be moved along a first line with respect to a base element, between a first longitudinal position and a second longitudinal position. In addition, a first offsetting device is provided which permits the printing of printed images offset from one another transversely with respect to the first line. The first offsetting device is configured to offset the print head relative to the print-head holder from a first transverse position into at least a second transverse position spaced apart from the first transverse position transversely with respect to the first line. In this case, the first offsetting device contains at least a first guide device with a first guide face and at least a second guide device with a guide element which cooperate, with mutual relative movement, in order to offset the print head from the first into the second transverse position by moving the print-head holder along the first line.
In the sense of the present invention, the term print head designates all types of printing devices which are able to produce a printed image on a medium. In other words, the term includes printing devices using any desired printing techniques. Nor is it intended to be restricted to the component which produces the printed image directly but, in addition, can contain further components which are needed to produce printed images. These may be, for example, ink storage containers, etc.
A generic device is disclosed for example by Published, European Patent Application EP 0 980 761 A1. In the device described there, the print head is disposed displaceably in a holder guided by a guide rod. For the purpose of printing, the holder, and therefore the print head, is moved along a first line, namely parallel to the guide rod.
Once a first printed image has been produced, the print head is offset relative to the holder at right angles to the first line, in order, in a second step, to produce a second printed image while moving the print head in the opposite direction along the first line. The offset of the second printed image in relation to the first printed image is so great that the two printed images overlap at most in the marginal area in which they adjoin each other transversely with respect to the first line. This makes it possible to use one print head to produce an overall printed image whose dimension transversely with respect to the first line, that is to say transversely with respect to the printing direction, corresponds approximately to twice the printing width of the print head.
In the known device, the offsetting device is implemented by a pin which is disposed on the underside of the print head and which, in order to offset the print head transversely with respect to the first line, is guided in a groove in the base element. The groove runs at an angle to the first line, so that in the event of relative movement between the pin and the groove along the first line, the offsetting movement of the print head at right angles to the first line is produced.
This configuration is associated with the disadvantage that the groove is relatively complicated to produce, since particularly close tolerances have to be complied with in order to achieve the desired transverse offset exactly. A further disadvantage resides in the fact that subsequent adjustment is impossible.
It is accordingly an object of the invention to provide a printing device with a transverse guide for offsetting a print head transversely with respect to the printing direction which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which requires little outlay, and permits rapid, high-quality printing.
With the foregoing and other objects in view there is provided, in accordance with the invention, a printing device. The printing device contains a base element, a print head, and a print-head holder displaceably holding the print head. In order to achieve a relative movement between the print head and a medium to be printed, the print-head holder is configured such that during printing the print-head holder can be moved along an imaginary line between a first longitudinal position and a second longitudinal position positioned above the base element. An offsetting device is provided and permits the printing of printed images offset from one another transversely with respect to the imaginary line. The offsetting device is configured to offset the print head relative to the print-head holder from a first transverse position to a second transverse position spaced apart from the first transverse position, and transversely with respect to the imaginary line. The offsetting device includes a first guide device with a first guide face and a second guide device with a guide element which cooperate, with mutual relative movement, in order to offset the print head from the first transverse position to the second transverse position by moving the print-head holder along the imaginary line. The guide element of the second guide device is disposed on the base element.
The invention is based on the technical teaching that a particularly cost-effective and easily implemented printing device is obtained if the guide element of the second guide device is disposed on the base element. Such a guide element disposed on the base element may be produced considerably more simply than the known guide groove.
For example, it can be formed simply by a simple guide pin with a circularly cylindrical operative face.
Furthermore, it is straightforwardly possible to adjust the guide element subsequently. For example, it can be disposed on the base element such that it can be adjusted transversely with respect to the first line. In addition, in order to achieve the positional adjustment, it is possible to configure the second guide device in the manner of an eccentric. For example, a guide pin with a circularly cylindrical operative face may be fixed such that it can be rotated about an axis located eccentrically.
The term guide device in the sense of the present invention includes any desired devices which, when they cooperate with an opposing part like the guide element according to the invention, influences the direction of the relative movement between the guide device and the opposing part.
In this case, the first guide device acts on the print head. For this purpose, it can be disposed directly on the print head. Alternatively, it can also be disposed on the print-head holder and act on the print head via appropriate operative elements for offsetting the latter.
In variants of the invention which are preferred, because they are simple to configure, the first guide device has at least a first guide face and the second guide device is formed by a guide element which cooperates with the first guide face in order to offset the print head. The first guide face is swept over by the guide element as the guide devices cooperate. In this case, the guide element can have a second guide face, over which the operative partner sweeps during the cooperation of the guide devices. However, it is likewise possible for the guide element to be configured such that a line or point contact with the first guide face results.
Provided that the contact, that is to say the action of a contact force, between the two guide devices is ensured, a defined movement of the print head during offsetting is also ensured. The contact force can be ensured, for example, by a spring acting on the print head.
The first guide device is preferably formed by a guide groove and the second guide device by a guide pin, since in this case the result is a configuration which is particularly simple to produce and provides reliable guidance. In addition, such a configuration ensures positive guidance, which also permits reliable guidance without any special prestressing of the two guide devices against each other. Preferably the guide pin has a circularly cylindrical operative face.
The first guide face runs at an angle to the first line. The course of the inclination of the first guide face, in particular of the guide groove, in relation to the first line can also be matched to the course of the contact force between the guide devices. This force may change over the offsetting movement, in particular in variants in which prestressing of the two guide devices against each other by a spring or the like is provided, which deforms more and more with continued transverse offset of the print head and therefore has the effect of a changing contact force between the two guide devices. Matching the inclination can be carried out with the effect that specific normal and/or tangential force limits in the contact area between the two guide devices are not exceeded. In this way, the wear on the guide devices can be kept low.
In preferred variants of the device according to the invention, the guide groove has a substantially V-shaped or Y-shaped course. This permits a reversal of direction along the first line as the print head is offset transversely with respect to the first line. This reduces influences of this reversal of movement on the accuracy of the offset. These influences may occur during the desired rapid movement through the offset region against the background of the fastest possible printing operation, because of an abrupt reversal of movement. As a result of the guidance further ensured after the reversal of movement in this configuration, such influences are reduced to a minimum. In addition, it goes without saying in this case that the limbs of the guide groove do not absolutely necessarily have to be configured to be rectilinear. They can also have a curved course.
The limbs of the V-shaped or Y-shaped guide groove are preferably disposed at an angle to the first line. This reduces the movement travel needed for the transverse offset of the print-head holder along the first line, which in turn has an advantageous effect on the overall size of the device. It is preferable for limbs of the guide groove to run substantially symmetrical to an axis parallel to the first line, since in this case, given a predefined inclination of the limbs to the first line, the shortest movement travel needed for the transverse offset is achieved.
In the transition region of the limbs of the guide groove, a guide device is then provided to ensure the offsetting movement from the first into the second transverse position. The guide device is configured such that, following the reversal of movement, the guide element passes through that region of the guide groove through which it has not yet traveled. This reliably rules out the situation where, following the reversal of movement, unintended resetting to the initial position takes place in that it is not the further course of the guide groove which is passed through, but that region of the guide groove which has just been passed through but is now passed through again in the opposite direction.
In this case, the guide device preferably contains a diverter device which is configured to close the first limb of the guide groove and open the second limb of the guide groove after passing the diverter device.
It is preferable for the guide device disposed on the base element and belonging to the first offsetting device to be disposed in the region of the first or second longitudinal position of the print-head holder, in order to permit the transverse offsetting of the print head directly after reaching the first or second longitudinal position of the print-head holder. This ensures the lowest possible overall height of the device and, also reduces the overall printing time because of the short paths to be traveled.
In preferred configurations of the device according to the invention, at least a second offsetting device is provided to offset the print head from the second into the first transverse position. This permits circulatory operation of the device, that is to say in order to reach the initial position of the print head, it is not necessary to travel through the offsetting device in the opposite direction.
The second offsetting device can be formed by a simple spring and a triggering device which resets the print head into the first transverse position, that is to say its initial position transverse to the first line, following the actuation of the triggering device.
In this case, the second offsetting device is preferably configured to offset the print head from the second into the first transverse position by moving the print-head holder along the first line, which also renders a separate drive superfluous.
In beneficial developments, the second offsetting device operates on the same principle as the first offsetting device. The second offsetting device preferably contains at least a third guide device. The third guide device is further preferably configured to cooperate with at least one of the guide devices of the first offsetting device, so that the provision of a separate guide device cooperating with the third guide device is rendered superfluous.
In advantageous variants, a guide device belonging to the first offsetting device is disposed on the base element in the area of the first longitudinal position of the print-head holder, and the third guide device is disposed on the base element in the area of the second longitudinal position of the print-head holder. Alternatively, a guide device belonging to the first offsetting device is disposed on the base element in the area of the second longitudinal position of the print-head holder, and the third guide device is disposed on the base element in the area of the first longitudinal position of the print-head holder. In both variants, the lowest possible overall size of the device is ensured. Further, the overall printing time is also reduced, because of the short paths to be traveled.
As a result of the configuration according to the invention, a separate drive for offsetting the print head transversely is dispensed with. Instead, the drive for moving the print head during printing is also used as a drive for the offsetting device.
By using simple guide devices that can be moved relative to one another, first, the outlay on construction for an appropriate device is reduced. Second, the mass of the printing unit, containing the print head and the print-head holder, which has to be moved during printing is also reduced, since the printing unit only bears on one of the guide devices. This in turn has a positive effect on the accelerations that can be achieved during high-quality printing, and therefore the achievable printing speed.
In accordance with an added feature of the invention, the second guide device is disposed on the base element such that its position can be adjusted transversely with respect to the imaginary line.
In accordance with an additional feature of the invention, in order to achieve a positional adjustment, the second guide device is configured as an eccentric.
In accordance with another feature of the invention, the second guide device is disposed on the base element in an area of one of the first longitudinal position and the second longitudinal position of the print-head holder.
In accordance with a further feature of the invention, a further offsetting device for offsetting the print head from the second transverse position to the first transverse position is disposed on the base element.
In accordance with another added feature of the invention, the offsetting device is configured to offset the print head from the first transverse position to the second transverse position by moving the print-head holder along the imaginary line.
In accordance with another additional feature of the invention, the further offsetting device contains a third guide device.
In accordance with another further feature of the invention, the third guide device is configured to cooperate with the first guide device belonging to the offsetting device.
In accordance with a concomitant feature of the invention, the printing device is a franking machine.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a printing device with a transverse guide for offsetting a print head transversely with respect to the printing direction, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.